The present invention relates to a technique for enhancing the performance of a high-frequency power amplifier module used in a communication mobile terminal or the like, and more particularly to a technique effectively applicable to anti-ESD (ElectroStatic Discharge) characteristic enhancement and harmonic suppression in a branching filter of the high-frequency power amplifier module.
Recent years have seen the widespread proliferation of mobile phones used as terminal units for mobile telecommunication, and at present, there is an increasing demand for implementation of more diverse functionalities in mobile phones. Regarding a high-frequency power amplifier module contained in a mobile phone, for example, it is desired to reduce the size thereof while providing refinement in harmonic suppression and enhancement in anti-ESD characteristic for wider-bandwidth communication.
In common practice, the high-frequency power amplifier module is provided with a branching filter such as a diplexer which is a filter for separating transmitting signals in transmission through an antenna and receiving signals in reception therethrough.
Thus, for example, transmitting and receiving signals of a low frequency band circuit of GSM (Global System for Mobile Communications) are prevented from straying into a high frequency band circuit of DCS (Digital Cellular System) or PCS (Personal Communication Service).
For high-frequency power amplifier modules of the above-mentioned kind, the following arrangements have been proposed: In the patent document 1 indicated below, for example, there is disclosed an arrangement in which an impedance phase relationship of two-fold higher harmonics is set up within a range of 180°±90° for a matching circuit and a lowpass filter with respect to a coupling point thereof, thereby transmitting fundamental waves with low loss while reducing two-fold higher harmonics to a desired level or below. In the patent document 2 indicated below, for example, there is disclosed an arrangement in which an ESD filter is provided between a lowpass filter of a low frequency band circuit and an antenna switch, thereby realizing favorable sensitivity of reception while removing static electricity.
Patent Document 1
    Japanese Unexamined Patent Publication No. 2004-032482Patent Document 2    Japanese Unexamined Patent Publication No. 2003-046452